1. Field of Invention
This invention relates generally to data storage, and more particularly to the data collection and storage of dynamic data, for example, in condition based monitoring of machinery conditions.
2. Description of Related Art
In condition based monitoring, two types of data are generally referred to when describing the system: static, and dynamic. According to known condition based monitoring standards, for example the API 670 standard, when discussing data associated with condition monitoring, a good initial separation is static versus dynamic. With a radial displacement probe, the static portion can be classified as an overall amplitude or with filtering and a speed reference can be broken into a filtered amplitude and phase, typically 1×, 2×, etc. If the dynamic portion of the data is also captured, additional information can be displayed in the form of time waveforms, orbits, spectrum, and many others. This differentiation is also applicable for velocity probes, accelerometers, load cells, microphones, strain gauges, and dynamic pressure transducers.
Static Data is data that describes the quantitative characteristics of the measured parameter. Static data can also include quantitative values describing the conditions under which the parameter was measured. For predictive maintenance purposes, static data is typically presented in various forms of trend plots and displays/lists of current values. Examples of static data include vibration amplitude, phase lag angle, frequency, average shaft position, shaft rotate speed, time, date, monitor alarm, and OK status. The static portion of a radial proximity probe should include the shaft position information, which is in the gap voltage. The combination of “x” and “y” shaft position information produces the Shaft Centerline Plot.
Dynamic Data is data (steady state or transient) which contain that part of the transducer signal representing the dynamic (e.g., vibration) characteristics of the measured variable. Typical dynamic data presentations include orbit, timebase waveform, spectrum, polar, bode, cascade, and waterfall plots. From this data, it is possible to derive static data signal parameters, such as amplitude; frequency filtered amplitude, and phase lag angle.
For static data there are known methods for efficiently storing this data. The inventor has discovered that this is not the case for dynamic data. A single waveform may contain numerous (e.g., 2048 or more) samples of raw data. This makes dynamic data often much bulkier than static data. Traditionally dynamic data is collected using two techniques. One technique is to collect a waveform at a fixed interval, typically two minutes or more in length. The second technique is to collect data on exception (delta rpm, alarm event, transient modes). When the exception occurs any and all waveforms buffered in a device are sent to the historian for storage. Following that waveforms are collected as fast as the device is capable until the exception state is completed. This approach to dynamic data collection leads to many terabytes of storage and many waveforms for users to look through.
Dynamic data can fill a large amount of hard drive space when trended over time. Initial calculations show that if a traditional approach to collection is used, where samples are stored at a fixed interval, many terabytes of hard drive space will be required each year just to hold all the data. Most of this data is the same, as machines generally run at a steady unchanging state. A large percentage of this data is not important to users as it is largely repeated values inefficiently taking up valuable storage space. Having the most important data, for example, when machine conditions change, is critical. For data collection the inventors have discovered an approach to automatically optimize data storage requirements, the amount of data (e.g., number of waveforms) collected, and the relevance of each data sample for improved data storage efficiency by distinguishing, selecting, collecting and storing the most important data without human intervention.
All references cited herein are incorporated herein by reference in their entireties.